The invention relates to a non-drug alternative to enhance cognitive function. In particular, the invention provides for exposing an extraocular (i.e., non-ocular) region of a human to light during sleep, which enhances REM sleep. Also provided are devices to carry out the methods. Key timing parameters ensure effective REM enhancement without adversely impacting a subject""s circadian clock. The invention provides for improving cognitive function and performance in healthy individuals and in individuals suffering from a disease or disorder in which mental status is compromised.
Rapid eye movement, or REM sleep, is a discrete sleep state characterized by muscle atonia (i.e., flaccid paralysis), low voltage, desynchronized EEG, and phasic activity such as increased respiratory activity, muscle twitches and burst of rapid eye movement. In humans, REM sleep comprises about 20-25% of a normal night""s sleep and it is during this time that dreams typically occur.
There is a vast body of literature documenting an intimate relationship between the occurrence of REM sleep on one hand, and learning and memory on the other. For example, rodents undergoing intensive water maze learning trials, and humans exposed to high-intensity learning and memory regimens exhibit increased REM sleep amounts in subsequent sleep episodes. Likewise, deprivation of REM sleep inhibits learning and memory on subsequent tasks and retention of learned information is compromised when followed by REM deprivation.
Presentation of auditory, visual, and somatosensory stimuli just prior to or during sleep has been reported to enhance REM sleep in laboratory animals and humans, typically without altering non-REM (NREM) sleep (Block et al., In: Neurobiology of Sleep and Memory, Drucker-Colin and MacGaugh, eds., New York: Academic Press, 1977, pp. 255-72; Drucker-Colin et al., Brain Res. 278:308, 1983; Guerrien et al., Physiol. Beh. 45:947, 1988; Mandai et al., Sleep ""86 Sutttgart: Gustav Fischer Verlag, 1988, pp. 3824; Merchant-Nancy et al., Brain Res. 681:15, 1988; Vazquez et al., Sleep 21:138, 1988). One sensory stimulus that has not been tested in this regard is photic stimulation. Although rats maintained in conditions of constant light exhibit more REM sleep per 24 hours (Vazquez and Neuhaus, J. Comp. Physiol. 128:37, 1978), there is no report of alteration of REM sleep by administration of a pulse of light during sleep. Naturally the disruptive effect on sleep of light administration to the eyes argues against conducting such a study at all.
In previous work, the inventors have shown that light applied to the popliteal fossa (the area directly behind the kneecap) can affect the biological clock in the same way as light presented to the eyes (co-owned, co-pending U.S. patent application No. 09/074,455 and International Application No. PCT/US98/09550, Publication No. WO 98/51372, filed May 7 and 11, 1998, respectively, both entitled xe2x80x9cNon-ocular Circadian Clock Resetting in Humansxe2x80x9d; Campbell et al., Science 279:376, 1998). However, there was no indication that non-ocular light exposure would in any way affect sleep stages or patterns, and particularly no indication that it could enhance REM sleep.
Moreover, the discovery that non-ocular light exposure can shift the circadian cycle cautions against doing anything that would unintentionally disrupt the circadian cycle in the absence of an external disruption, such as trans-meridian travel or shift work.
As described below, the present invention advantageously permits enhancement of REM sleep, and concomitant enhancement of cognitive function. Moreover, by applying the strategies and devices of the invention, these enhancements can be achieved without adversely modifying the circadian rhythm.
The present invention advantageously provides a method for enhancing REM sleep in a subject, preferably a human subject. The method comprises exposing a non-ocular region of a subject to photic stimulation for an interval during a sleep period. In particular, this method can increase the number of minutes spent in REM sleep during the interval of photic stimulation, e.g., by increasing the frequency of REM periods. The method of the invention advantageously provides for enhancing cognitive function in a subject, particularly memory processes. Subjects whom the invention can assist include those who suffer from a medical disorder in which mental status is compromised, as well as normal individuals.
In a specific embodiment, the invention provides a method for increasing REM sleep of a person, which method comprises the steps of sensing the start of the REM cycle; sensing the end of the REM cycle; determining the time and interval of the REM cycle; and, augmenting the time interval of the REM cycle by selectively providing non-ocular photic stimulation for a predetermined interval. Also provided is a device or an article for increasing REM sleep of a person. Such an article, which may be adapted to be worn or attached to the person, includes a sensor which provides phasic activity signals; a timing circuit connected to the sensor and outputting an elapsed-interval signal indicative of the magnitude of the REM cycle; a comparator which compares the elapsed-interval signal to a predetermined-interval signal and outputs a shortfall signal; a controller responsive to the shortfall signal to generate a control signal; and, a photic stimulator positionable in contact with the person""s skin and being actuated in response to the control signal.